This invention relates to an optical head assembly for adjustably mounting a read/write laser and a monitoring photodiode(s).
In video disks, digital audio disks and the like, used as media for recording information, an information signal is recorded by forming pits in a spiral track corresponding to the information signal through irradiation of the record surface of the disk with a fine spot of light. When the information signal thus recorded is to be reproduced, the original information signal is reproduced corresponding to the change of reflected or transmitted light by irradiation of the track with a spot of light.
Various types of optical head assemblies for performing such recording and reproduction include a light emitting element such as a semiconductor laser, an objective lens for spot focusing the laser light onto the record surface of the disk, and light receiving elements such as photodiodes for receiving light reflected from the record surface of the disk to generate an output information signal.
FIG. 7 shows a member used in a conventional optical head assembly, in which a semiconductor laser 51 formed as an element in a chip is housed in an airtight package 55 constituted by a cylindrical casing 52, a glass plate 53 and a cover 54, and is connected to terminals 56 by wiring (not shown). The member, together with other optical members, is attached to a body 57 as shown in FIG. 8. FIG. 9 shows another member used in the conventional optical head assembly, in which photodiodes 59 and 60 formed in a chip are sealed within a package 61 formed by molding resin, and are connected to terminals 62 by wiring (not shown). This member is also attached to the body 57 as shown in FIG. 8. The relative positions of the semiconductor laser and photodiodes are adjusted with high accuracy so that the light reflected from the record surface of the disk 64 after emission from the laser 51 can enter the photodiodes 59 and 60 exactly.
The relative positional adjustment is carried out in three orthogonal directions, i.e. the direction of the path of incident and reflected light, and directions perpendicular to such path and to each other.
For the purpose of the positional adjustment, the packages 55 and 61 supporting the laser 51 and photodiodes 59 and 60 are attached to the body 57 through intermediate positioning members (not shown) provided with guide grooves formed in each adjustment direction. The grooves are slidably fitted to guide projections formed on the body 57 to enable the movement of the intermediate members in any one or more of the aforementioned three directions. Each of the intermediate members is guided by the grooves exactly in the three axial directions, so that each of the packages 55 and 61 is guided exactly. As a result, the adjustment of the relative positions of the semiconductor laser 51 and photodiodes 59 and 60 mounted in their respective packages can be carried out with a high degree of accuracy.
The laser 51 and the photodiodes 59 and 60 in themselves are very small parts, but the packages 55 and 61 surrounding them and the intermediate members are relatively large. Further, the packages and the intermediate members are disposed at predetermined intervals on the body 57. Accordingly, the body 57 supporting the packages and the intermediate members also becomes a large member. This causes difficulties in miniaturizing the optical head assembly.
Further, to adjust the relative positions of the laser and the photodiodes conventionally, a large number of intermediate positioning members must be interposed between the packages and the body. Accordingly, the number of parts increases to make it difficult to reduce the optical head assembly in size and cost as a whole.